Self-adjusting hydraulic actuator



March 12', 1940. H. D. coLMAN SELF-ADJUSTING HYDRAULIC ACTUATOR FiledFeb. 25, 1937 Patented Mar. 12, 1940 UNITED STATES inc'lElaT OFFICE2,193,190 sELr-AnJus'rrnG HYDRAULIC Ac'rUA'ron Howard D; Colman,Rockford, Ill.

Application February es, 1931,ser1alNo.127.154 l l.

30 Claims.

The present invention relates generally to improvements in hydraulicactuators for brakes, and the like, and has particular reference to anactuator -that is self-adjustable to maintain automatically apredetermined release clearance regardless of wear.

One of the objects of the present invention is to provide a brakeactuator having novel means for trapping a predetermined body of' liquidwhich serves as a stop to limit the release movement, and which isautomatically adjustablev in volume-to dene the desired releaseclearance.

. Another object is to provide a hydraulic brake actuator having a newand improved release clearance adjuster which affords an extensive Wearrange limited only by the maximum extent of movement of the actuator,and which is adapted to eifect minutely graduated adjustments tocompensate accurately for wear.

Afurther object is to provide a trapped liquid clearance adjuster whichis operable to effect adjustments in either direction as required tomaintain the predetermined release clearance.

Still another object resides in the provision of. an automatictrapped-liquid clearance adjuster which is operable to relieve excessivepressure, such, for example, as might result in an automotive vehiclebrake in the event of an over-adjustment due to drum contraction afterexpansion from heat.

A further object resides in the provision of a new and improvedhydraulic brake actuator having a hermetically sealed pressure applyingelement, and having means for automatically trapping an adjustable 4bodyof the actuating liquid within the element to maintain a predeterminedrelease clearance.

Various general objects reside in the provision of an automaticclearance adjuster of the foregoing character'which-is housed within theactuator,` and which is simple and inexpensive in construction, andeiicient, reliable and sensitive in operation.

Further objects-and advantages will become apparent as the descriptionproceeds.

In the accompanying drawing, Figure 1 is a fragmentary side view of ahydraulic automotive vehicle brake having an automatic clearanceadjuster embodying the features of my invention.

Fig. 2 is a fragmentary longitudinal sectional view of the brakeactuator taken along line 2-2 of F'lg'; 1, and illustrating the partsinthe position occupied during brake release.

Fig. 3 is a fragmentary sectional view similar to Fig. 2, butillustrating the parts in the posi-' (Cl. 18s-152) tion occupied aftertake-up of the brake clearance.

Fig. 4 is a fragmentary sectional view similar to Fig. 2', butillustrating the parts in the position occupied during brakeapplication.

Fig. 5 is a transverse sectional view on a reduced scale taken alongline 5--5 of Fig. 2.

Referring more particularly `to the drawing, the self-adjuster forcompensating for wear is especially adapted for, and hence shown, in aspecific arrangement in connection with a hydraulic automotive vehiclebrake. It is to be understood, however, that the invention in various ofits broad aspects is not limited to any particular form of brake norarrangement therein, but is adapted for various kinds and types ofbrakes and similar devices, and is intended to4 vcover all equivalent,modied or alternative constructions and adaptations coming within thespirit and scope of the appended claims.

The brake selected for purposes of illustration, comprises a cylindricaldrum 6 adapted for rotation with a wheel (not shown), and substantiallyclosed at one end by a removable backing plate 1. Two arcuate brakeshoes 8 and 9, with a suitable brake lining, are pivotal into engagementwith the interior of the drum 6. The free ends of the shoes 8 and 9 areoperatively related to a hydraulic actuator II) interposed therebetweenand rigidly mounted as by means of lugs II and bolts I2 to the backingplate 1. A tension spring I3 is connected at opposite ends to theshoes 3and 9, and tends to retract them out of engagement with the drum 6.

The brake actuator I0 is of the double end type having oppositely actingpressure applying elements for spreading the shoes .8 and 9. Since theopposite ends of the actuator I0 are substantially alike, only one endthereof, as illustrated in Fig. 2, will be described in detail. YThepressure applying element for actuating the shoe 8 may be of anysuitable character, and is herein shown as of the hermetically sealedtype disclosed in my copending application Serial No. 118,205, ledDecember 30, 1936. More particu- "larly, the pressure applying elementcomprises a diaphragm or bellows `which may be made of a suitableresilient or flexible material, such as rubber or a rubber composition,and which is in the form of a cup I4 dening an internal pressure chamberI5 adapted to receive brake liquid under pressure from a suitable sourceof supply such, for example, as a pedal operated mastei actuator (notshown). The cup I4 has an axially extensible and contractiblecylindricalwall II of uniform and constant diameter reenfrced externallyto resist the pressure ofthe brake liquid in the chamber l5, andconnected at one end with a liquid-tight seal to a hollow body or basemember I1. The'bottom of the cup I4 is closed by a liquid-tightreenforced transverse'wall constituting a brake applying head I8 axiallymovable/'in response to the reversible pressure differential between theforce of the return spring I3 and the pressure of the brake liquid. Inaction and function, the head I8 is comparable to a piston having aconstant ef. fective pressure area, and hence the cup I4 is hereinafterreferred to as a piston bellows.

The base member I1 constitutes the stationary body of the actuator I0.It is formed with a central supply and relief chamber. preferably a fbore I9, which opens to the interior of the brake bellows I4, and whichhas an inlet and discharge passage 20 leading to the liquid source.

To provide for the liquid-tight connection with the piston bellows I4,the base member I1 is formed at one end and concentrically about thebore I9A with an annular flange 2I and with an annular groove 22 justwithin and at the base of the Iiange. The bottom ofthe groove 22 isstepped, with the inner marginal portion relatively shallow and smoothlycurved toward the face of the base member I1, and with the outermarginal portion relatively .deep and rounded as indicated at 23. Thefixed end of the wall I6 is formed with an external annularV ilange 24which seats' in and conforms in shape to the groove 22, an outerperipheral rib or bead 25 .closes and extends in concentrically spacedrelation to the wall I8, and is formed on its inner 'end with anexternal peripheral flange 38 disposed against the anchor ring 28. Therings 26 to 28 and flange 38 are riveted in position by upsetting themetal of the base member I1 over the outer edge of the ilange 38 asindicated at 3l, thereby clamping the ange 24 of the wall I6 in positionunder a heavy deflection pressure to provide a hermetic seal. v

The piston head I8 comprises an internal annular flange 32, on themovable end of the wall I6, which is formed with a rib or bead 33' atthe inner periphery, and which is clamped under aheavy deection pressurebetween two opposed rigid disks 34 and 35. The inner disk 34, which isthe same in` diameter as the interior of the wall I8, has an axialthreaded sleeve 38 extending snugly through the flange 32 for endabutment with the disk 35, and is formed about the iiangeA with anannular groove 31 adapted to receive the rib 33.' 'Ihe disks 34 and 35are secured together as by means of a screw bolt '384 threaded into thesleeve 38 to clar..p Athe flange 32 therebetween. The iiange 32 is soformed that when free from deiiection itis somewhat smaller 'in diameterthan the external diameter of the wall I8 and is somewhat thicker thanthe space between the disks 34 and y35. However, when the screw bolt 38is tightened The cylindrical wall I8 is confined against radialdeformation by means of a reenforcement 39 which is rigid andnondeformable diametrically but readily extensible and contractibleaxially,

and which is interposed between the wall I6 and the tube 29. Thereenforcement 39 may be made of any suitable material such, for example,as strip steel, and may be provided in various forms. In the presentinstance, the rings or convolutions are generally Z-shaped in crosssection with the legs of adjacent convolutions overlappingto provide alost motion connection. One end of the reenforcement 39 is nonrotatablyanchored to the ring 28. The other end of the reenforcement 39 isnonrotatably anchored to a `cupshaped member 40 in which the disk 35 isseated and which is formed with a diametrical rib 4I engaging acomplementary groove 42 inthe free end of the brake shoe 8. A ilexiblebellows 43 is; tightly secured at opposite ends respectively to the shoe8 and the outer end of the tube 29, and prevents the entry of dirt, gritand other foreign matter, and the escape of 'lubricant from thereenforcement 39.

It will be understood that in the operation of the actuator I0, fluidunder pressure is supplied .through the passage 20 to the chamber I 9and from there to the interior of the brake bellows I4. Thereupon, thepiston head I8 is actuated to apply the brake shee 8, this movementbeing permitted by axial extension of the wall I6. 'I'he reenforoement39 aiords a rigid peripheral support for the wall I5, but permitsextension and contraction upon the application of a very light force.The-range of axial movement is comparatively small 'so that the diameterremains substantially constant. Friction between the wall I6 and thereenforcement 33 is 'practically eliminated. By reason of thesubstantially uniform spacing of the successive rings or convolutions'ofthe reeniorcanmt 3|,the rubber 0r other material of which the wall I5 ismade is not subjected to objectionable crimping. bending, pinching orexcessive distention, thereby preventing physical injury and internal ormolecular friction.

One of the primary features of the invention resides in limiting thereturn ow of the brake actuating liquid from the brake bellows I4 uponrelease of the brake so as to maintainautomatically a constant brakingclearance regardless of wear on the brake shoes 8 and 9. The means Iforthis purpose includes a normally closed valve '44 which is disposedbetween the supply chamber is and the chamber l5, and which is under thecontrol of the hydraulic pressure in the brake system. The arrangementis such that when the hydraulic pressure rises to a predetermined valuesuillcient to take up the normal brake clearance,

'the valve 44 will open, and conversely when the pressure drops to thisvalue, the valve will close. As a result, an unrestricted ow of theliquid is permitted to apply the heavy brake pressure, but upon brakerelease the valve 4 4 closes to trap a body of the liquid in the chamberI5 of such volume that retraction of the shoes 8 and 9 is limited to apredetermined clearance.

In the preferred form, the valve 44 comprises a stationary annular seat45 and an axially movable valve member 48. The seat 45 is formed on oneend of a sleeve 41 which denes a central now mage 48, and which isrigidly connected, as by a press t, to an encircling annular disk 49. Aperipheral rib 58 on the sleeve 41 engages one side of the disk 43 toresist the closing pressure of the valve 44. The disk 49 in turn isrigidly supported in the outer end of a valve housing in the form of a.longitudinally split tube I. Preferably, an internal annular groove 52in the tube 5I interiits with the outer peripheral margin of the disk49.

The tube 5I extends centrally into the piston bellows I4, and issuitably supported at its base end on an annular cup 53. In the present'i'nstance, an internal annular groove 54'in the tube 5I interflts with aperipheral ilange 55 on the rim of the cup 53. It will be understoodthat the assembly is effected by expanding the tube 5I against the forceof its resiliency to receive the disk 49 and the ange 55, and thenmoving the latter respectively into registration with the -grooves 52and 54, whereupon the tube will contract to lock the interiitting partssecurely together.

'I'he base of the cup 53 has a bottom wall 56 formed with suitableapertures 51 for the passage of the brake liquid, and is inserted intoan end enlargement 58 of the supply chamber or bore I9. To providesuitable locking means, the cup 53 is formed with an external peripheralgroove 59 adapted to receive a resilient split ring 6l) projecting froman annular groove 6I in the bore enlargement 58. Preferably, the innerside of the groove 59 and the corresponding side of the ring 6I) areinclined so that the cup 53 is held in a fixed position against a curvedshoulder 62 at the inner end of the bore enlargement. It will beunderstand that when 4the cup 53 is inserted into the bore enlargement58 the curved base edge will act to expand the ring 60 into the groove6I, and that when the cup is in position the ring will contract andhence snap into the groove 59 to complete the assembly.

I'he valve member 46 comprises a pressure responsive bellows ordiaphragm, preferably in the form of a rubber cup having an axiallycontractble and extensible cylindrical wal-l 63 anchored at one endtothe wall 56. In the present instance, the stationary end ofthe wall 69is formed with an internal annular ange 64 which is positioned in aperipheral dovetail groove 65 in a disk 66 riveted to the wall 56, andwhich is clamped thereby under deflection pressure against the wall 5I5.The movable end of the wall 53 is closed by atransverse wall 61 which isadapted for-` engagement with the valve seat 45 and hence denes thevalve face. -A disk 68 of rigid material is disposed against the insideof the end wall 61, and serves as a reenforcing backing for the latter.A coiled compression spring 69 is disposed Within the cup against theinterior of the wall 63 and in opposite end abutment with the disks 66and 68, and tends to urge the end wall 61 into engagement with the valveseat 45.

It will be evident that the valve bellows 46 is sealed internally underatmospheric pressure,` and is exposed externally to the pressure of thebrake liquid. The spring 69 not only tends to close the valve 44, butalsov affords an internal peripheral reenforcement for the peripheralwall 63. Hence, the diameter of the wall 63 remainsconstant, and themovable end wail 61 defines the effective diaphragm area. Fixed to thedisk 66 and extending therefrom almost through the spring 69 is a tube'IIJ which serves'to prevent buckling of the spring, and the free end ofwhich constitutes a stop for the disk 69 to limit the opening movementof the valve member 46.

If desired, a guide ring 1I may be mounted in the tube 5I to support andcenter the movable tile force of the spring I3.

a bottom or end wall 15 anchored to the seatI sleeve 41. The inner endof the sleeve 1'4 is coniined under deflection pressure, by the adjacentend of the tube 5I and the cup 53 and iiange 55, within an annular4notch 16 formed in the base member I1 and opening peripherally to theouter end vof the bore enlargement 58. Also, the inner peripheral edgeof the end wall 15 is formed with an enlarged rib or bead 11 which isconfined under deflection pressure by a disk 16 within a dovetail notch19 in the periphery of the sleeve 41 at the base of the disk 49.

The sleeve 14 has a free form slightly less in diameter than the tube5I, and hence normally encircles the latter under tension, and isreenforced internally thereby against the pressure of the liquid in thechamber I5. However, the sleeve 14 is distensibleby the pressure of theliquid which may pass through suitable openings in the tube 5I such asthe longitudinal split 89. During initial brake application, and untilthe valve 44 opens, the distension sleeve 14 serves to transmit theapplied liquid pressure, in excess of the residual pressure of thetrapped liquid, to the latter, thereby equalizing the pressure on thevalve face 61 at opposite sidesof the annular valve seat 45.

The end wall 15 serves as a clearance diaphragm having a limitedreversible movement between the disks 49 and 18 to permit a slightdisplacement of the trapped liquid after closure of the valve 44. Thedisks 49 and 'lare vdished or concave to provide a good backing for theclearance diaphragm 'l5 in either position of adjustment, and are sospaced that the trapped liquid displacement will permit retraction ofthe brake shoes 9 and 9 through the desired clearance upon brakerelease. Suitable openings 8l are formed in the disks 49 and 18 for thefree passage of liquid so that the clearance diaphragm 'l5 will beresponsive to any pressure diii'erental. The diaphragm 15 has a freeform to the left of a greater curvature thanthe disk 18, and normallytends to engage the latter as illustrated in Fig. 4.by reason ofdistortion pressure. It will be understood that the disks 49 and 18 maybe formed and spaced to provide the proper displacement for pistonbellows I4. of various sizes.

In operation, the'parts assume the positions illustrated in Fig. 2 whenthe brake is off. Under this condition, the valve 44'is closed bythespring 69 in opposition to the residual pressure P of the trappedliquid which is determined by the retrac- The brake liquid in thechamber I9 and up to the valve 44 is under a zero or low initialpressure P1 less than the pressure P. Hence, the distention sleeve 14engages the tube 5I, and the clearance diaphragm 'I5 is flexed againstthe inner stop disk 49.

Toy apply `the brake, liquid under increasing pressure is supplied tothe chamber I9, but cannot pass to the chamber I5 so long as the valve44 is closed. When the pressure P1 equals the pressure P, the diaphragm15 will ilex intochgagement with the disk 1 8, as illustrated in Fig. 3,to move the brake shoes 8 and 9 through the normal clearance into lightengagement with the drumi. As the pressure P1 continues to rise.

"of the seat 45.

the sl'eeve 14 will distend to equalize the pressureacting on the valveface 61 at opposite sides Shortly thereafter, the liquid pressure willcompress the valve bellows 46 against the action of the spring YG9 toopen the valve 44 as illustrated in Fig. 4, and cause the sleeve I4 toreturn into engagement with-the tube 5I. The brake'liquid is now free topass directly into the chamber I5 in any volume required to apply thebrake with full pressure.

To release the brake, the chamber I9 is relieved, thereby resulting in aprogressive pressure drop, and an attendant flow oi.' liquid from thechamber I5 through the valve u, due partially to previous distortion ofthe parts and particularly the drum 6. When the pressure drops to apoint where the shoe 8 is about to leave the drum 6, the valve 44 willclose, thereby trapping a denite bodyof liquid in the chamber I5. Thepressure P1 will continue to drop, while the pressure P of the trappedliquid will be determined by the retractile force of the spring I 3which is insuicient toA overcome the valve spring 69. When the pressureP1 falls below vthe pressure P,

'the clearance diaphragm 15 will be flexed by the single application ofthe brake.

It will be evident that I have provided a novel clearance adjuster forhydraulic brakes which utilizes a trapped body o'f the brakev liquid asa retractile stop. The adjuster is not subject to mechanicaldisadvantages, such as frictional variy ations, limitations as to rangeand adjustment increments, and objectionable space requirements. Therange of adjustment is unlimited within the maximum extent of movementof the actuator Il, and the adjustment increments may be innitesimal orof any size as required'to obtain an accurate compensation for wear.

'I'he adjuster is especially adapted for use in hermetically sealedbraking system wherein no loss of liquid from 'the trapped body pastthepiston 'mechanically into engagement with said drum,

said actuator unit including means therein auto.- matically operable totrap a predetermined body of brake liquid therein. to limit theretractile movement of said wall and said element and to increase ordecrease said body of liquid as' required to maintainl a predeterminedclearance All brakes of the vehicle are adjusted separately anduniformly.

after each brake actuation regardless of brake wear and brake drumexpansion and contraction.

2. A hydraulic power actuator for brakes and the like comprising, incombination, a hollow base deiining a liquid supply chamber, a yieldablehermetically sealed cup closed at the outer end and connected at theother end to said base for communication with said chamber, van axiallyextensible and contractible reenforcement encircling said cup andanchored at opposite ends respectively to said base and formovement witlthe outer end of said cup, an antibuckling tube mounted on said base andclosely encircling said reenforcement, and means automatically operablebelow a predetermined liquid pressure to trap a body of liquid in saidcup.

3. A hydraulic power actuator for brakes and the like comprising, incombination, a hollow base deiining a liquid supply chamber, a yieldablehermetically sealed cup closed at the outer end and connected at theother end to said base for communication with said chamber, an axiallyextensible and contractible reenforcement encircling said cup andanchored at opposite ends respectively to said base and for movementwith the outer end of said cup, and normally closed valve meanscontrolling the communication between said chamber and said cup, andadapted to open in response to a rise in liquid pressure to apredetermined value.

4. A hydraulic power actuator for brakes and the like comprising, incombination, a hollow base dening a liquid supply chamber, a yieldablehermetically sealed cup having a' movable closed pressure transmittingend and having a liquid tight connection with said base forcommunication with said chamber, and normally closed valve means mountedwithin said cup and controlling the passage of liquid between saidchamber and said cup, said valve means having a stationary seat and aspring seated valve member pressure responsive to open upon apredetermined increase and to close upon a predetermined decrease in thepressure in said chamber.

5. A hydraulic power actuator for brakes and the like comprising, incombination, a hollow base defining a liquid supply chamber, a yieldablehermetically sealed piston bellows having a closed movable end and beingin communication with said chamber, and an axially extensible andcontractible reenforcement for said bellows and anchored at oppositeends respectively to said base and for movement with said movable end ofsaid bellows, lsaid reenforcement comprising a coilA having a spiralgroove in one edge and a spiral ange on the other edge engaging in saidgroove.-

6. A hydraulic actuator for effecting pressure application of a movablemember against a retractile force, said actuator comprising, incombination, a pressure chamber including a movable pressuretransmitting wal1\adapted for loperative association with said member, aliquid supply chamber adapted to be placed under a varying liquidpressure, and means including a sealed partition wall between saidchambers reversibly movable in response to reversal of pressurediiferences in said chambers and including a normally closed valve forcontrolling communication between said chambers in response to theliquidV pressure in said supply chamber, said valve being adaptedautomatically to open and close respectively at liquid pressure in saidpressure chamber above and below a predetermined pressure in excess ofsaid retractile force.

' '7. A hydraulic actuator for effecting pressure application of amovable member against a retractile force, said actuator comprising, incombination, a pressure chamber including a movable pressuretransmitting wall adapted for operative association with said member, aliquid supply chamber adapted to be placed under a varying liquidpressure, a partition between said chambers and including a stationaryvalve seat deiining a iiow passage between said chambers, and a movablevalve member normally spring-urged against said seat in opposition tothe pressure in said pressure chamber and adapted to open in response toa predetermined pressure rise in said pressure chamber.

8. A hydraulic actuator for eiecting pressure application of a movablemember against a retractile force, said actuator comprising, incombination, a pressure chamber including a movable pressuretransmitting wall adapted for operative association with said member, aliquid supply chamber adapted to be placed under a varying liquidpressure, a valve for controlling communication between said chambersand having a stationary valve seat and a normally spring seated valvemember, and a pressure responsive element independent of said valvemember for transmitting liquid-pressure from saidv supply chamber tosaid pressure chamber when said valve is closed, said valve beingadapted to open in response to a predetermined pressure rise in saidchambers, and opening in a direction counter to the flow of liquid fromsaid supply chamber to said pressure chamber.

9. A hydraulic actuator system for eiecting pressure application of amovable member against a retractile force, said actuator systemcomprising, in combination, a pressure chamber including a movablepressure transmitting wall adapted for operative association with saidmember, a liquid supply chamber adapted to be placed under la varyingliquid pressure, a valve for controlling communication between saidchambers and adapted to close in response to a predetermined pressuredrop in said chambers to trap a body of liquid in said pressure chamber,and means independent of said valve and responsive to a further pressuredrop in said supply chamber to effect a predetermined enlargement ofsaid pres-V sure chamber.

10. In a hydraulic actuator, in combination. with a liquid supplychamber, a pressure chamber adapted for communication with said `supplychamber, a power applying element movable in response to the pressure insaid pressure chamber, and means for retracting said element, a,

clearance adjuster including a normally closed valve controlling saidcommunication, said valve being adapted to open in a direction oppositeto the liquid ow from said supply chamber to said pressure chamber inresponse to a predetermined rise in the liquid pressure in said pressure,chamber and to close in response to a predetermined drop in the liquidpressure in said pressure chamber, whereby a `body of liquid will betrapped in said pressure chamber under a normal residual pressuredetermined by said retracting means and normally insufficient to opensaid valve to limit the extent of the retractile movement of saidelement, said valve however being adapted to open directly in responseto an excessive residual pressure to relieve said trapped body ofliquid.

11. In a hydraulic actuator, in combination with a liquid supplychamber, a pressure chamber adapted for communication with said supplybody of liquid to cause said body to shift and i flow passage openingthrough said wall, said parvalve controlling said communication, saidvalve 5 being adapted to open in response to a predetermined rise in theliquid pressure and to close in response to a predetermined drop in theliquid pressure, whereby a body of liquid will be trapped in saidpressure chamber vunder a residual pressure determined by saidretracting means and insufficient to open said valve, and pressureresponsive means operable upon a drop in pressure in said supply chamberbelow that of said trapped thereby permit retraction of said` elementthrough a predetermined distance.

12. In a hydraulic actuator, in combination with a liquid supplychamber, a pressure chamber adapted for communication with said supplychamber and including a brake applying element movable in response tothe pressure in said pressure chamber, a flexible partition wall betweensaid chambers, a stationary valve seat defining a tition wall having adistention sleeve and a reversibly movable clearance diaphragm,reenforcing means for supporting said distention sleeve against thepressure in said pressure chamber, spaced meansior hunting the movementof said clearance diaphragm and for backing up tne latter in eitherextrme position of adjustment, said diaphragm in its free form normallybeing flexed toward said pressure chamber, and a valve member in saidsupply chamber and normally engaging said seat to interrupt saidcommunication, said valve member comprising a hermetically sealedbellows having an axially extensible and contractible peripheral walland an end wall defining a valve face, and a coiled compression springsupporting the interior of said cylindrical wall and tending to urgesaid valve member into closed position.

13. In a hydraulic actuator, in combination with a liquid supplychamber, a pressure chamber 45 adapted for communication with saidsupply .chamber and including a brake applying element movable inresponse to the pressure in said pressure chamber, a stationary valveseat having a ovv passage for establishing communication be- 5( tweensaid chambers, a exible partition wall between said chambers, astationary valve seat dening a ow passage opening through said wall,said partition wall having a distention sleeve and a reversibly movableclearance diaphragm, reen- 5I forcing means `for supporting saiddistention wall against the pressure in said pressure chamber, spacedmeans for limiting the movement of said clearance diaphragm and forbacking up the latter in either extreme position of adjustment, said 6|diaphragm in its free form normally being iiexed toward said pressurechamber, and a valve member in said supply chamber and normally engagingsaid seat to interrupt said communication,

said valve member being adapted to open in res,

spouse to a predetermined pressure rise in said supply and pressurechambers.

14. A hydraulic actuator for effecting pressure application of a movablemember against a retractile force, said actuator comprising, in com- 7.bination, a pressure chamber including a movable pressure transmittingwall adapted for operative association with said member, a liquid supplychamber adapted to be placed underl a varying liquid pressure, apressure responsive clearance 7 diaphragm between said chambers andmovable reversibly between two xed positions in response to a reversibledifferential between the pressures in said chambers, and having a freeform normally tending to cause movement toward said pressure chamber,and a valve controlling communication between said chambers and adaptedto close upon a pressure drop to a predetermined point to trap a body'ofliquid in said pressure chamber, said diaphragm being movable towardsaid supply chamber after closure of said valve to shift said trappedbody of liquid.

15. A hydraulic actuator for eiecting pressure application of a movablemember against a retractile force, said actuator comprising, incombination, a pressure chamber including a movable pressuretransmitting wall adapted for oper- Y ative association with saidmember, a liquid supply chamber adapted to be placed under a varyingliquid pressure, a pressure responsive clearance diaphragm between saidchambers and movable reversibly between two fixed positions in re'sponse to a reversible dinerential between the pressures in saidchambers, and a normally closed valve controlling communication betweensaid .chambers and adapted to openupona predetermined pressure rise insaid supply chamber.

16. A hydraulic actuator for effecting pressure application of a movablemember against a retractile force, said actuator comprising, incombination, a pressure chamber including a movable pressuretransmitting wall adapted for operative association with said member, aliquid supply chamber adapted to be placed under a varying liquidpressure, a valve controlling communicationv between saidchambers andincluding a xed valve seat dening a now-passage and a pressureresponsive valve member having a yieldable pressure face for engagingsaid seat, a reversibly movable clearance diaphragm interposed betweensaid chambers, and spaced stop disks mounted in fixed positions atopposite sides of said clearance diaphragm. f'

17. A hydraulic actuator for eilecting pressure application of a movablemember against a retractile force, said actuator comprising, incombination, a pressure chamber including a movable pressuretransmitting wall adapted for operative association with said member, aliquid supply chamber adapted to be placed under a varying liquidpressure, a valve controlling communication between said chambers andincluding a iixed valve seat defining a iiow passage and a pressureresponsive valve member having a yieldable pressure face for engagingsaid seat, a deection diaphragm for transmitting liquid pressure fromsaid supply chamber lto said pressure chamber when said'valve is closed,and a stationary rigid backing for limiting movement of said diaphragmtoward said supply chamber, said deection dia-g phragm having afree formnormally tending to effect engagement with said backing.

18. A hydraulic actuator for eecting pressure application of a movablemember against a re-.y

tractile force, said actuator comprising, in combination, a pressurelchamber including a movable pressure transmitting wall adapted for oper-.tractile force, said actuator comprising, in combination, a pressurechamber including a mov-` able pressure transmitting wall adapted foroperative association with said member, a liquid supply chamber adaptedto be placed under a varying liquid pressure, a valve controllingintercommunication between said chambers and including a stationaryvalve seat, and a pressure responsive valve member consisting of ahermetically sealed cup having an end wall movable into and out ofengagement with said seat, spring means normally urging said valvemember-toward said scat and reenforcing the peripheral wall 'of saidcup, an antibuckling 'tube Within said spring means and acting as 'astop to limit the extent of valve opening, and external guide means forthe movable end of said valve member.

20. A hydraulic actuator for effecting pressure.

application of a movable member against a retractile force, saidactuator comprising, in combination, a pressure chamber including 'amovable pressure transmitting wall adapted for operative associationwith said member, a liquid supply chamber adapted to be placed under avarying liquid pressure, a valve controlling intercommunication betweensaid chambers and including a stationary valve seat, and a pressureresponsive valve member consisting of a hermetically sealed cup havingan end wall of constant area movable into .and out of engagement withsaid seat, and spring means normally urging said valve member towards'aid seat, said valve being adapted to open against the action of saidspring ,means upon a predetermined rise in the liquid pressure acting onsaid end wall.

21. In a hydraulic actuator, in combination with a stationary support, amovable valve member comprising, in combination, a cup having acontractible and extensible peripheral wall hermetically sealed at oneend to said support and 22. In a hydraulic actuator, in combination bercomprising, in combination, a cup having a contractible and extensibleperipheral wall hermetically sealed at one end tosaid supprt and closedat the other end by a transverse wall deilning a pressure face ofconstant area, and means tending to extend ysaid peripheral wall inopposition to external pressure on said face.

23. In a hydraulic actuator, in combination with a stationary support; amovable valt/e member comprising, in combination, a cup'having acontractible and extensible peripheral wall connected at one end to saidsupport and closed at vthe other end by a transverse wall dening apressure face oi constant area, and a coiled compression spring withinsaid cup for reenforcing l extensible and contractible peripheral wallcon.

said peripheral wall against external pressure. and tending to elongatesaid peripheral wail against pressure acting on said face.

24. A hydraulic power actuator for brakes and the like comprising, incombination, a base dening a fluid supply chamber, a hermetically sealedcup of yieldable material havingan axially extensible and contractibleperipheral wall connected at one end to said base and closed at theother end by an axially movable transverse wall, A

said transverse wall comprising an' inner peripheral flange of resilientmaterial with an enlarged rounded bead at the inner edge, anl internaldisk having a central sleeve extending through said flange and anencircling groove receiving said bead, an external disk engaging theouter face of said flange, and means for clamping said external diskagainst said sleeve to secure saidilange with a liquid tight seal underdeiiectlon pressure between said disks, and means for supporting saidperipheral wall against radial distention by internal pressure.

25. A hydraulic power actuator for brakes and the like comprising, lincombination, a base delining a iluid supply chamber, a hermeticallysealed cup of yieldable material having an axially nected at one end tosaid base and closed at the other end by an axially movable transversewall, said transverse wall comprising an inner peripheral flange oi'resilient material with an enlarged bead at the inner edge, an internaldisk having a groove receiving said bead, an external disk engagingthe'outer tace o! said flange, and means for clamping said diskstogether to secure said ange with a liquid'tight seal under deflectionpressure between said disks.

26. A hydraulic power actuator for brakes and the like comprising, incombination, a base deiining a uid supply chamber and provided on oneside about said chamber with an annular groove and an encirclingcentering iiange, a hermetically sealed cup of yieldable material havingan axially extensible and contractible peripheral wall closed at one endby an axially movable transverse pressure transmitting wall, the otherend of said peripheral wall comprising an external peripheral resilientflange with an enlarged bead at the outer edge seated in said groove,and disk means centered by said en circling ange for clamping saidperipheral' ilange in said groove under deflection pressure to provide akliquid tight seal. A

27. In a hydraulic actuator, in combination, a base having a liquidsupply chamber opening to one side thereof and having an annular groovein said side about said chamber, a perforated cup mounted in saidchamber and having aperipheral ange in axially spaced relation to saidgroove, a split tube connected at one end to said flange, a perforatedannular disk secured in the other end oi said tube, a central valve seatrigid with said disk anddening a ilow e. a second disk rigid with saidseat in opposed relation to said first mentioned disk, a peripheralgroove in said seat between said disks, a yieldable distention sleevenormally `snugly encircling said tube, a bead on one end of said sleevesecured unde deilection pressure in said annular groove by said cup -andtube, a transverse clearance diay phragm integral with the other end ofsaid'sleeve and having a bead at its inner edge secured in saidperipheral groove under deflection pressure by said second disk, anaxially extensible and 1 contractible pressure responsive valve membermounted at one end on said cup and having a pressure face normallyengaging said seat, and means'deflning a pressure chamber adapted forcommunication through said ilow passage with the interior of said tube,and having a movable 'pressure responsive element.

28. A hydraulic system for effecting pressure application of a movablemember against a retractile force,'said system comprising, in combi- 1nation, a pressure chamber including a movable pressure transmittingwall adapted for operative association with said member, a liquid supplychamber adapted to beconnected to said pressure chamber and to be placedunder a varying liquid pressure, a pressure responsive clearance elementinterposed between said chambers and movable reversibly between twofixed 'positions in responseto a reversible pressure diierential betweenthe pressures in said chambers, and a normally closed valve controllingcommunication .between said chambers and adapted to mined pressure risein said supply chamber.

29. A hydraulic system for eecting pressure application of a movablemember against a retractile iorce, said system comprising, incombination, a pressure chamber including a movable pressuretransmitting wall adapted for operative association with said member, aliquid supply chamber adapted to be in communication with said pressurechamber and to be placed under a varying liquid pressure, a valvecontrolling communication between said chambers and having an open upona predeterannular valve seat deilning a iiow passage anda pressureresponsive valve element movable axially into and out of engagement withsaid 4seat and when closed being exposed to the pressure in saidpressure chamber, and pressure responsive means for transmitting thepressure in said suplsaid flange, and Vmeans for clamping' said diskstogether to secure said flange with a liquid tight seal under deflectionpressure between said disks.

HOWARD D. ooLMAN.

